Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

Wed
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Another round of snow and wind will continue to stress the snowpack on Tuesday. Give the snowpack time to heal by avoiding slopes over 35 degrees, convexities, or wind-loaded terrain where triggering an avalanche is more likely. With so much snow, any avalanche is capable of growing large enough to be fatal.

Problemi valanghivi

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Very Likely
    Dimensione
    2

    This storm cycle has had fluctuating snow levels, wind direction changes, varying wind speeds, and periods of light and intense precipitation over the past few days. This has created multiple density breaks and potential failure points in the recent storm snow, and we’re not done with the snow yet. On Saturday, one of these breaks (2/11) was particularly reactive, as slabs were remotely triggered and propagating far distances. We haven’t seen as much action on this layer since, but it could still be active in some areas, causing slabs to fail in surprising ways. Take the time to dig and look for heavy snow over weak snow and those potential failure points. Your common travel tests like hand pits, test slopes, and uptrack tests will only work for the uppermost layers and may not paint the full picture. Take note if these upper layers are failing or you see shooting cracks, but be sure to look a little deeper to see what else you can find. If you find signs of unstable snow or see recent avalanches, you should stay off slopes over 35 degrees and be aware of avalanche terrain above you.

    (2/15/2021) This small Storm Slab was triggered by a skier near White Pass on Monday morning (2/15) as temperatures began to warm. [SW 4700', Cortwright Butte; SS-ASc-R2/D1-N]

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    3

    The snowpack will continue to get stressed through additional snow and wind on Tuesday, and the potential for very large deep persistent slabs remains possible. The weak snowpack structure that has been hanging around our zone the last few weeks has not gone away and is now well over 5 feet deep. You should continue to stay away from big, steep, or open slopes, particularly at upper elevations. At all elevations, put a large buffer between you and large avalanche paths, particularly ones prone to wind-loading where this layer may be activated more easily.

    (2/6/2021) This slab was intentionally triggered by a small cornice drop on Saturday (2/6) in the Crystal backcountry. It propagated widely and is believed to have run on the Mid-January crust/facet combo. [E aspect, 6300'. Photo: Jeremy Allyn]

Avalanche Discussion

The widespread natural avalanche cycle we were expecting on Monday and Monday night should run its course before Tuesday begins. That doesn’t mean that you won’t see a natural avalanche or that conditions aren’t dangerous. If they occur, natural avalanches will be more likely during periods of high precipitation or wind. If you find that the weather fits this description and naturals are occurring all around you, the avalanche hazard may be heightened and you should avoid all avalanche terrain. 

Even without natural activity, slopes are now primed for human triggered avalanches that will be large enough to bury and kill you. On Sunday, temperatures warmed and heavier snow fell on top of low-density snow, creating an “upside-down” snowpack in many locations. With winds set to increase on Tuesday afternoon, you could find wind-loaded terrain contains fresh and reactive slabs. Other areas may still contain unconsolidated snow, creating the potential for Dry Loose avalanches or “sluffs”. These loose slides often seem harmless, but they can entrain snow and have reportedly triggered a few slabs over the weekend. If an avalanche is able to step down to trigger a failure on the Mid-January crust, avalanches will be very large and most likely fatal for anyone caught in their path. With so much recent snow, complex and overlapping avalanche problems, and limited observations, we are not without uncertainty about conditions, particularly as you ascend in elevation. What we do know is that it is deep out there and the snowpack is going to need time to adjust to this new load. Continue to be patient and keep your terrain choices dialed back during the final stages of this storm cycle.

You also need to recognize that so much recent snow can be a hazard on its own. Learn more about snow immersion hazard here.

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

Regioni coperte